Devonian Shales of Northern Ohio. 191 



the Chagrin shale which as a surface formation lies mainly east 

 of Cleveland, originated in a sea older than and distinct from 

 the one in which the darker shales of the same group west of 

 Cleveland were deposited. The advocacy of this hypothesis 

 appears to rest essentially on two kinds of evidence. These 

 briefly stated are (1) fannal and lithologic differences between 

 the shale of northeastern Ohio and the shale of the Huron 

 River region and (2) discordance in direction of dip between 

 the Cleveland shale and the Devonian limestone base of the 

 Ohio shale group. These facts of course are not new. New- 

 berry, Orton and others who considered the Chagrin and the 

 black shales to the westward synchronous deposits were doubt- 

 less familiar with them owing to their intimate acquaintance 

 with the geology of Ohio. We have, therefore, to consider 

 only a new interpretation of well-known facts. 



We may inquire, first, whether the differences in the kind 

 and amount of organic remains which distinguish the fauna 

 found in the Chagrin from that in the Cleveland and Huron 

 shales are of such a character as to indicate that the two faunas 

 lived in distinct seas, as the overlap theory assumes. Paleon- 

 tologists who are familiar with the work of marine zoologists 

 know that in the present seas a particular fauna may be found 

 to follow the coast-line within the limits of shallow coastal 

 waters for hundreds of miles and yet disappear completely in 

 deeper water a few miles to seaward off any part of the coast. 

 The bathymetric limitation of fannal distribution is a fact of 

 the utmost importance to the paleontologist and one too often 

 lost sight of when differences in faunas are offered as evidence 

 of overlap and distinct age. Risso, the naturalist of the seas 

 of Nice, was perhaps the first to call attention to that distribu- 

 tion of marine life which is dependent upon depth. Goodwin- 

 Austin has concisely stated this principle of the distribution of 

 marine life in the following words: 



" The sublittoral zone of every sea and ocean presents the 

 fullness of its fauna and from that it decreases progressively and 

 rapidly . . . ."* 



A good specific illustration of the general principle is given by 

 Jeffriesf from the Mediterranean Sea. In the Bay of La 

 Spezia, in the eastern Mediterranean, Mr. Jeffries, after de- 

 scribing the rich and varied fauna at slight depths, continues : 

 " For several leagues seaward in from fifteen to forty fathoms 

 I met with nothing but tenaceous mud with Turritella com- 

 munis and a curious variety of Calyptrcea sinensis. 1 '' Here 

 we find in the eastern Mediterranean a molluscan fauna, which, 



* Goodwin-Austin. Eobert : Nat. Hist, of European Seas, 1859, p. 246. 

 f Nat. Hist, of European Seas. 



